1. Field of the Invention
The present invention relates generally to an electronic editing apparatus. More specifically, the invention relates to an apparatus for performing color frame editing.
2. Description of the Prior Art
In general, in editing a video tape, a desired portion of an original video tape is reproduced onto a master tape at a desired portion thereof. A time code signal is generally recorded on a video tape in the longitudinal direction thereof for indicating and detecting the tape position (tape time). Thus, the time code data for the editing start point, that is, the in-point of the original tape, and the time code data for the editing start point of the master tape are stored in the memory of an editing apparatus.
Therefore, before starting the actual editing operation, an in-point is determined for use in each of VTRs and then each tape is positioned at a pre-roll point in each of the VTRs. The pre-roll point is a tape position located ahead of the in-point by, for example, 5 seconds of tape running time. Thus, during the editing operation, the tape begins running from the pre-roll point in each of the VTRs.
When the two VTRs bearing the original and master tapes are started, time codes are read from the respective tapes of the VTRs. The difference between each of the read-out time codes and the time code at each of the respective determined in-points is calculated, and the running of the original tape, that is, the phase thereof, is controlled so that the values of the above differences are the same. When the differences are both zero, the VTR for the master tape is operated in its recording mode to record a desired video signal reproduced from the original tape.
In other words, during the time period in which the pre-roll portion of each tape is running past the heads of the VTRs, a control operation is carried out so that the values of the time codes for the respective registered in-points are made equal. Since a time-code is provided corresponding to every frame of a picture, the time intervals, within which the respective tapes arrive at their in-points are made equal and frame synchronization is established by controlling the movements of the two tapes. Therefore, synchronizing signals are continuous from the video signal previously recorded on the master tape and the video signal newly recorded from the original tape so that the editing operation can be performed with no picture disturbance.
If a color video signal is recorded subsequent to a prerecorded color video signal, it is necessary that the subcarrier of the color video signal is also continuous from the previously recorded color video signal to the newly recorded color video signal in order to assure that the displayed picture has the correct hue. The process for keeping the continuity of the subcarrier at the editing point is called color frame editing.
As is well known, the phase of the color subcarrier signals of a color television signal in an NTSC system shifts through 4 fields in one cycle. On the other hand, in the PAL system, the phase of the subcarrier signals of the color television signal shift through 8 fields in one cycle. In order to indicate each of the phase shift cycles of the color subcarrier signals of the color television signal, a recurring index signal is superimposed on a control signal (CTL signal) and is recurrent for a given number of fields, e.g. every four (4) fields in the NTSC system, eight (8) fields in the PAL system. The index signal will be hereafter referred to as a "color framing pulse or a color frame pulse". Based on the color framing pulse, the subcarrier phase in each field, which will be hereafter referred to as the "color frame phase" in the color subcarrier phase shifting cycle which will be referred to as the "color frame cycle" can be derived.
In the conventional color frame editing operation utilizing the CTL signal superimposed on the color frame pulses, the time code signal and the color framing pulses reproduced from the playback video tape recorder and the recording video tape recorder are supplied to an edit control apparatus in order to detect a synchronous condition of the video tape recorders. As is well known, a plurality of types of information are supplied to the edit control apparatus in addition to the time code signals and the color framing pulses. Therefore, in order to synchronize the playback video tape recorder and the recording video tape recorder, cables, connectors and so forth for transferring the color framing pulses are required. In addition, in order to detect the color framing pulses, an additional electronic circuit is required in the edit control apparatus. This makes the editing control apparatus bulky and complicated in construction.